Utility knives with extendable blades are known. Utility knives with blades that automatically retract into a handle are also known. However, such utility knives are often cumbersome or unwieldy, or suffer from deficiencies in the mechanism that is used to extend the blade. Accordingly, it would be useful to be able to provide cutter apparatuses that facilitate easy, safe and comfortable blade extension, as well as user-selectable blade extension lengths. It would also be useful to be able to incorporate the aforementioned features into multifunctional cutter apparatuses.